hi joe, i suggest you turn your sine wave amplitude up to 1Vpp or so. 20 mVpp is about 1% of full scale, and perhaps that's what you are seeing, depending on how you interpret the adc data. if you are interpreting as 2's complement, then you are seeing 0, -1, 0, -1, at the correct frequency, and roughly the correct amplitude.
you might also want to try injecting your sine wave into other inputs, in case you've got the wrong one, and the waveform is weaking coupling into the input you are plotting. best wishes, dan On Tue, Mar 25, 2014 at 6:33 AM, Kujawski, Joseph <[email protected]>wrote: > I have a simple design which pipes the input of one of the ADC16 channels > to the 1GbE block to be recorded on an external computer. The clock input > for the ROACH board is set to 200MHz and there is a 20MHz, 20mVp-p, AC > coupled input to channel A1 of the ADC (verified on an oscilloscope). > Reading the values sent across the 1GbE, I get the following: > > 255 > 255 > 255 > 255 > 255 > 0 > 0 > 0 > 0 > 0 > 255 > 255 > 255 > 255 > 255 > 0 > 0 > 0 > 0 > 0 > > Which looks like the ADC is saturating, however, the CASPER documentation > indicates that the full scale input of the ADC is 2V p-p. > > For reference, I have successfully transferred counter data through the > ethernet port, so I know that this interface is capable of transferring > values besides x00 and xFF. > > Does anyone have suggestions as to how to fix this problem? > > -Joe Kujawski > >
